Ertapenem sodium is a carbapenem marketed by Merck as Invanz®, and has chemical name [4R,5S,6S]-3-[[(3S,5S)-5-[[(3-carboxyphenyl)amino]carbonyl]-3-pyrrolidinyl]-thio]-6-[(1R)-1-hydroxyethyl]-4-methyl-7-oxo-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylic acid.
Ertapenem of formula (I) is a 1β-methylcarbapenem antibiotic, and used as antibiotic agent in the treatment of moderate to severe complicated foot infection due to indicated pathogens in diabetic patients without osteomyelitis, Ertapenem is also useful in the treatment of pneumonia, urinary tract infections, intra-abdominal, gynecological, skin, and soft tissue infections, meningitis, septicemia and febrile Neutrogena.
In view of the importance of the compound of the formula (I), several synthetic procedures to prepare the compound have been reported.
U.S. Pat. No. 5,478,820 and U.S. Pat. No. 5,856,321 claim various processes for preparing Ertapenem and its sodium salt. Example 12 of U.S. Pat. No. 5,478,820 discloses a process in which the Ertapenem was isolated by using column purification as well as freeze-drying technique. According to Example 4 of this patent disodium salt of Ertapenem was prepared by dissolving crude product in water using NaHCO3, followed by purification using column chromatography and subsequent lyophilization
U.S. Pat. No. 6,504,027 provides a process for preparing Ertapenem in crystalline form which comprises deprotecting and extracting a polar organic solution containing a crude mono-protected Ertapenem of formula
                wherein P represents protecting groupwith C4-10 alcohol in the presence of ion-pairing reagent followed by adjusting the pH to 5.5, collecting and crystallizing the resultant aqueous phase to produce a crystalline compound. Since this patent involves number of operations like extraction, this process industrially not viable.        
U.S. Pat. No. 7,145,002 provides a process for producing Ertapenem or its sodium salt and/or its solvate in crystalline form.
The processes reported in these patents yielded only crystalline compound of Ertapenem or its salt further the said patents utilize a temperature in the range of −5 to −10° C. for crystallization; none of the prior art processes discloses precipitation processes for producing amorphous form of Ertapenem of formula (I). More particularly the above said patents provide only precipitation process for preparing Ertapenem monosodium in crystalline form not its disodium sodium.
With our continued research for developing a process for the preparation of compound of formula (I), we have come up with a process, which is not only commercially viable, but involves simple purification techniques such as crystallization and yields the compound of formula (I) in amorphous form.